there is a lot of snow on the snowy road, especially in the north of China. If the snow on the road is not cleared in time, it will easily lead to vehicle skidding and even a series of traffic accidents. Then why do you sprinkle salt on the road in snowy days? What salt is sprinkled on the road in snowy days?
Why salt should be sprinkled in snowy days
After snowing, the road surface is very slippery, which is easy to cause traffic accidents. The reason why salt is sprinkled on the road surface is that salt melts and water releases a lot of heat, which can make the snow melt as soon as possible, not easy to make the ground ice. If salt is sprinkled on the ice to melt and water releases heat, it will also make the ice melt, so that the friction of the ground is increased, which can reduce the occurrence of traffic accidents.
The principle of snow and salt
It starts with the chemical composition of the salt.
The salt is potassium chloride, and the snow is water. Potassium chloride is a water-soluble chemical. Potassium chloride dissolves in water to form potassium chloride aqueous solution, which contains potassium ion and chloride ion. When water is to be frozen, when there are chloride ions and potassium ions, chloride ions and potassium ions will destroy the crystal network structure of water, so that water can not be frozen. In other words, salt keeps snow from freezing.
In addition, the chapter of chemistry about vapor pressure introduces: in fact, snow is constantly melting and solidifying, but the speed of the two is equal, so it remains solid all the time! We all know that the freezing point of salt water is lower than that of water. After salt is sprinkled, the water around the snow will become salt water, so it can't solidify! So the snow will continue to melt, but it can't solidify again, so it's less and less!
Besides, salt is cheap and pollution-free. Therefore, when it snows, salt is often sprinkled on the road surface to prevent the snow water from freezing and the salt can melt the snow.
However, due to the erosion of roads caused by salt water, at present, many countries have not allowed to use the way of salting snow, but use snow melting agent to melt snow!
Disadvantages of snow and salt
The salt composition of snow melting is mainly potassium acetate and chlorine salt, which can easily cause metal rust when contacting with the metal without protective layer directly. This principle is the same as that when there is no clean brush and water in the iron pot, rust will be produced quickly.
There are some anti-corrosion measures for the car body surface, mainly to isolate the contact between the metal and the external substances, such as the painting of the car body surface, wax injection into the cavity of the car body frame, etc. In the case of complete protection, the snow melting agent will not cause too much damage to the car body, but if the protective layer is damaged, such as the car body paint is damaged (small collision accident leads to paint damage) for a long time without treatment, or the chassis is scratched due to the chassis bottom, etc., it will lead to the direct contact of metal with external substances, which may cause rust. If there is snow melting agent This will intensify the process.
Therefore, it is inevitable for vehicles in Northeast China to contact with snow melting agent, but the temperature rises after spring, so it is recommended that car owners conduct a thorough body cleaning including chassis.
How to melt snow in snowy days
If the snow on the road is not removed in time, it will become ice and bring danger to the driving car, so it should be removed.
The freezing point of normal water is 0 ℃, but after adding salt (NaC1, not necessarily salt), the freezing point of water decreases to less than 0 ℃, which is the reason for salt snow. But there are two disadvantages in this way. One is that the freezing point is limited, and the freezing point can not be reduced in too cold weather. Second, the salt has corrosive effect on the road and damages the road surface after long-term use.
So now many cities use special snow remover. Snow remover and salt can reduce the freezing point of water similarly, but the specific implementation process is different. It is mainly through the water absorption of the deicing agent and a large amount of heat release when melting that the structural lattice in the snow is dislocated, leading to the melting of ice and snow. After the ice and snow melt, it absorbs heat and makes the surrounding temperature drop. At this time, the vapor pressure of the solution is less than that of the ice and snow. In order to achieve a new balance, promote the continuous melting of the ice and snow, and form a solution, thus reducing the freezing point of the water, under the low temperature condition, the above-mentioned complex movement balance process is carried out repeatedly, which is the principle of deicing and snow melting.